The term "emulsion"as used herein means either a lotion that is liquid or semi-liquid or a gel.
The skin is the largest organ in the human body. It serves primarily as protection of the body against the environment. The skin is constantly exposed to the damaging effects of ultraviolet radiation, chemicals, and surroundings that are either too dry or too moist.
Protection against ultraviolet radiation can be provided by avoiding exposure to sunlight and/or using creams or other preparations providing protection from the sun. The skin protects itself by producing sebum (tallow) by the sebaceous glands and, to a much smaller extent, by the fat formed through the keratinization of the cells. The activity of the sebaceous glands is controlled by hormones and is reduced with age. Consequently, the fat supply of the skin is often insufficient in older people.
Skin fat is partially removed by hygienic procedures, such as washing, bathing or showering, particularly those portions that are most frequently washed, such as hands and face. In the case of low humidity, as in extreme cold, the unprotected skin suffers loss of moisture. The skin dries out and painful skin cracks can result. On the other hand, prolonged contact with water, particularly when the water's surface tension is strongly reduced by soap or synthetic detergents, causes skin damage through maceration.
The cosmetics industry has sought to relieve drying out of the skin through so-called moisturizers. These moisturizers generally are an oil-in-water emulsion, a water-in-oil emulsion, or mixed emulsions. They contain emulsifiers which facilitate the penetration of water and the removal of the dried-out fat film by washing. These preparations only partially limit trans epidermal water loss of the skin. The moisture retention of the skin is therefore unsatisfactory.
Petrolatum, on the other hand, can, to a great extent, limit the water loss of the skin (see, e.g., "Cosmetics and Toiletries" 93, pg. 27 (1978)). However, this effect is not totally one of reduction of the trans epidermal water loss by occlusion, but rather is based upon a pharmacological effect of the petrolatum grease on the skin. Petrolatum grease, however, is most unsatisfactory from a cosmetic standpoint because of its high viscosity. It penetrates poorly into the skin and adheres to it insufficiently, so that it is easily removed mechanically and by washing. Furthermore, it may be applied only with difficulty because of its high viscosity, so that an unpleasant greasy and sticky layer is formed.
It is known that certain petrolatums can irritate the skin and can also produce acanthosis of the epidermis. The properties mentioned come mainly from the components of petrolatum boiling below 180.degree. C. at 2 mbar (see, e.g., Schaaf, "Probleme der dermatologischen Grundlagenforschung," pg. 105 (1969)). The low-irritation fraction, because of its high viscosity, is only poorly capable of being distributed over the skin and is, consequently, cosmetically unsatisfactory.
In contrast, the petrolatum fractions utilized in accordance with the present invention, from which the more volatile oils (known to those of ordinary skill in the art as "white oils") have to a large extent been separated, have been found non-irritating to the skin.
Little pharmaceutical, cosmetic, veterinary or horticultural attention has been paid to the application of petrolatum fractions that exceed liquid petrolatum and petrolatum in molecular weight, viscosity and melting point. The higher molecular weight, higher viscosity, higher melting point fractions from that of higher viscosity Petrolatum, U.S.P. grades to highly viscous semi-solids and solids are very difficult, uncomfortable and anesthetic in application. In addition, they do not have the intrinsic ability to significantly contact the pores or surface layers of the substrates to which they are being applied. The addition of these highly viscous petrolatum fractions results in greasy or oily residues that can attract dirt and other pollutants. The addition of conventional solvents, such as mineral spirits, results in solutions that are unacceptable or unsafe for human, animal or horticultural use.
U.S. Pat. No. 4,355,046, to Suess, which is incorporated herein by reference, discloses admixing the high molecular weight petroleum fractions with certain volatile siloxanes, preferably octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and/or hexamethyldisiloxane.
The composition disclosed in the '046 patent is an admixture of approximately 10% to 90% by weight of high molecular weight petroleum fractions in which the white oil content does not exceed approximately 20% and approximately 90% to 10% by weight of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and/or hexamethyldisiloxane.
The compositions that are disclosed in the '046 patent are highly hydrophobic, not dispersible or soluble in water and are very viscous. Thus, the user needs to exert more than usual application energy to rub them into the substrate.
What is needed is a composition that contains the beneficial high molecular weight petroleum fractions and, at the same time, is easy to apply to a surface. Such a composition would have wide acceptance. In addition, the trans epidermal moisture loss would be reduced, thereby assuring natural moisturization of the drier horny layer of the skin.